CA1148331A - Method of removing sulfur dioxide - Google Patents
Method of removing sulfur dioxideInfo
- Publication number
- CA1148331A CA1148331A CA000338335A CA338335A CA1148331A CA 1148331 A CA1148331 A CA 1148331A CA 000338335 A CA000338335 A CA 000338335A CA 338335 A CA338335 A CA 338335A CA 1148331 A CA1148331 A CA 1148331A
- Authority
- CA
- Canada
- Prior art keywords
- alkali
- sulfite
- sulfate
- sulfosuccinate
- scrubbing solution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
- B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Biomedical Technology (AREA)
- Environmental & Geological Engineering (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Treating Waste Gases (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
METHOD OF REMOVING SULFUR DIOXIDE
ABSTRACT OF THE DISCLOSURE
A method of removing sulfur dioxide from an exhaust gas containing the same with an aqueous scrubbing solution containing alkali sulfite and alkali sulfosuccinate.
ABSTRACT OF THE DISCLOSURE
A method of removing sulfur dioxide from an exhaust gas containing the same with an aqueous scrubbing solution containing alkali sulfite and alkali sulfosuccinate.
Description
33~
The present invention concerns a ~ew method of removal of sulfur dioxide from an exhaust gas containing the same. In -the context of the present invention, the -term "alkali" means Na , NH4 and their mixtures.
According to the prior art, gaseous sulfur dio~ide (SO2) is absorbed into an aqueous scrubbing solution containing an alkali sulfite, the thus formed alkali hydrogen sulfite is brought into reaction with calcium carbonate and then the thus formed and separated calcium sulfite is filtered off to be removed from the system, the filtrate being circulated to the step of absorp-tion of SO2-Aqueous solutions containing alkali sulfite are excellentin absorbing SO2 and are used widely. ~Iowever, the alkali sulfite is partially oxidized by oxygen contained in the exhaust gas to become alkali sulfate having no ability to absorb SO2 and the thus formed alkali sulfate.gradually accumulates in the aqUeQus scrubbing solution to reduce the SO2-absorbing ability of the : aqueous scrubbing solution. Accordingly, in order to continue the operation of absorption of SO2, it is necessary to remove the thus accumulating alkali sulfate and at the same time to re-plenish the alkali sulfite.
The prior art has attempted to address the problem in the following ways:
(1) discharging from the system part of the scxubbing solution in circulation and supplying new alkali sulfite, alkali hydroxide or alkali carhonate to the system;
' 3~
The present invention concerns a ~ew method of removal of sulfur dioxide from an exhaust gas containing the same. In -the context of the present invention, the -term "alkali" means Na , NH4 and their mixtures.
According to the prior art, gaseous sulfur dio~ide (SO2) is absorbed into an aqueous scrubbing solution containing an alkali sulfite, the thus formed alkali hydrogen sulfite is brought into reaction with calcium carbonate and then the thus formed and separated calcium sulfite is filtered off to be removed from the system, the filtrate being circulated to the step of absorp-tion of SO2-Aqueous solutions containing alkali sulfite are excellentin absorbing SO2 and are used widely. ~Iowever, the alkali sulfite is partially oxidized by oxygen contained in the exhaust gas to become alkali sulfate having no ability to absorb SO2 and the thus formed alkali sulfate.gradually accumulates in the aqUeQus scrubbing solution to reduce the SO2-absorbing ability of the : aqueous scrubbing solution. Accordingly, in order to continue the operation of absorption of SO2, it is necessary to remove the thus accumulating alkali sulfate and at the same time to re-plenish the alkali sulfite.
The prior art has attempted to address the problem in the following ways:
(1) discharging from the system part of the scxubbing solution in circulation and supplying new alkali sulfite, alkali hydroxide or alkali carhonate to the system;
' 3~
(2) removing al]cali sulfate in the form of gypsum (CaSO4 2H2O) by using calcium sulfite and sulfuric acid according to the following reaction (I):
M2SO4 + 2 CaSO3 1/2 H~O ~ H2S4 + H2O
~ 2 MHSO3 -~ 2 CaS04 2 H20 ............. .... (I) wherein M is alkali;
M2SO4 + 2 CaSO3 1/2 H~O ~ H2S4 + H2O
~ 2 MHSO3 -~ 2 CaS04 2 H20 ............. .... (I) wherein M is alkali;
(3) converting alkali sulfate into sulfuric acid and a]kali hydroxide by electrolysis; or
(4) con~erting sodium sulfate into sodium hydroxide ~nd gypsum using slaked lime (Ca(OH)2) according to the following reaction (II):
Na2SO4 + Ca(OH)~ ~ 2 H2O ~ 2 NaOH -~ CaSO~ 2 H2O ...(II).
The latter is commonly used in practice.
However, the above-mentioned various methods have dis~
advantages as discussed below.
Method (1) causes the loss of expensive alkali source;
method (2~ necessitates the use of expensive sulfuric acid; method (3) is apt to be affected by a very small amount of impurities and necessitates a pre-treatment; and method (4) is only able to supply the regenerated sodium hydroxide in concentrations as small as 0.05 mol/kg, in the case where the alkali is sodium, because of the equilibrial nature of the reaction ~II) and the small solu-bility of slaked lime in the solution. As mentioned above, these customary methods are not satisfactory. In addition, since the afore-mentioned methods necessitate lar~e-scale facilities, they are not preferable from the economic viewpoi,nt~
In the accompanying drawings, Figure 1 shows the differ-' ' ' : ' ~ . . :
., 33~
ent changes in pH during the absorption of SO2 between two kindsof scrubbing solutions having different compositions;
Figure 2 shows the relation between the concentration ratio of S042 to S032 and the amount of gypsum separated out, and Figure 3 is a schematic outline illustratin~ a pxeferred embodiment of the present invention.
The inventors have found that under certain conditions, the alkali sulfate by-product may ~e double-decomposed with cal-cium carbonate to gypsum making it unnecessary to add a specialstep of removing alkali sulfate. Such conditions are that (1) alkali sul~osuccinate is used together with alkali sulfite as the SO2-absorbing agent, (2) the concentration of sulfit:e ion in the aqueous scrubbing solution ls controlled to be lower than 0.5 mol/kg and (3) the molar concentration ratio of sulfate ion to sulfite ion (SO4 /S032 ) is maintained at more than 3.
In the case of double decomposit1on of alkali hydrogen sulfite formed by the absorption of SO2 into an aqueous scrubbing solution of alkali sulfite with calcium carbonate, the concen-tration ratio of SO4 to SO3 in the aqueous scrubbing solution is required to be more than 3, preferably more than 4, in order to separate out gypsum in an equivalent amount to the amount of alkali sulfate formed in the system.
By contrast with this invention, in the case where only alkali sulfite is used as an SO2-absorbing agent, the concentra-tion of alkali sulfite is required to be 8 to 12~ by weight with .
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the concentration ratio of SO4 to SO3 more than 3, and accord-ingly, the total concentration of salts in the aqueolls solution becomes too large for salts to be deposited in the sys-tem, and in the case where an aqueous solut~on contains only alkali sulfo-succinate as an SO2~absorbing agent, the pH value of said aqueous solution drops rapidly when only a small amoun-t of SO2 is ab-sorbed.
~ ccordingly, in the case where only alkali sulfite is used as an absorbing agent with the ratio of sulfate to sulfite more than 3, the concentration of alkali sulfite must be less than 8% by weight, preferably less than 5~ by weight in the absorbing liquid. In such a case where the concentration of the absorbing agent is low, the amount of SO2 absorbable E?er unit amount of the scrubbing solution is small and it is necessary to provide a large amount of the scrubbing solution in order to raise the absorbing capacity. ~t is not preferable to use such a large amount of scrubbing solution.
In the method of the present invention, the concentration of sulfite ion in the scrubbing solution is controlled to less than 0.5 mol/kg and an alkali sulfosuccinate of a large solubil-ity in water is made co-present with the alkali sulfite. The alkali sulfosuccinate is equally ef~ective in absorbing SO2 and in forming aLkali hydrogen sulfite as alkali sulfite. The method of the present invention is advantageous in that by the co-presence of alkali sulfosuccinate with alkali sulfite, the possi-bility of salts separating out is removed and the concentration ratio of SO4 to SO3 can rlse above 3. Moreover, it becomes .: .
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possible to prevent the reduction of SO2-absorbing capacity of the scrubbing solution.
As a substance which may be co-present with alkali sul-fite in the aqueous scrubbing solution, alkali ac2tate, alkali propiona-te and others are sui-table candidates. However, it is inevitable that these alkali salts of organic acids to hydrolyze as a result of absorbing SO2, the organic acids so-formed being volatilized with the treated exhaust gas. Accordingly, it becomes necessary to wash th.e treated exnaust gas with water or an aqueous alkali solution to remove the ~olatilized organic acid, which renders the process more complicated.
Owiny to the molecular construction o~ sulfosuccinic acid, even after alkali sulfosuccinate is brought into contact with the exhaust gas containing SO2 and the aqueous scrubbing solution containing alkali sulfosuccinate absorbs the SO2, the free form of sulfosuccinic acid does not form in the scrubbing solution.
The sulfonic group of the acid remains always in ionic form (-SO3 M ) dissolved in the aqueous scrubbing solution. Accord-ingly, no free sulfosuccinic acid evaporates from the aqueous scrubbing solution when it is brought into contact with the ex-haust gas. This makes it unnecessary to install any additional step for the recovery of the free oryanic acid.
Accordiny to the present invention, it is possible to reduce the concentration of alkali sulfite in the scrubbing solution without reducing the SO2-absorbing capacity of the scrubbing solution, and the ratio o~ S042 to SO3 may he in-creased to more than 3 without making the total concentration of
Na2SO4 + Ca(OH)~ ~ 2 H2O ~ 2 NaOH -~ CaSO~ 2 H2O ...(II).
The latter is commonly used in practice.
However, the above-mentioned various methods have dis~
advantages as discussed below.
Method (1) causes the loss of expensive alkali source;
method (2~ necessitates the use of expensive sulfuric acid; method (3) is apt to be affected by a very small amount of impurities and necessitates a pre-treatment; and method (4) is only able to supply the regenerated sodium hydroxide in concentrations as small as 0.05 mol/kg, in the case where the alkali is sodium, because of the equilibrial nature of the reaction ~II) and the small solu-bility of slaked lime in the solution. As mentioned above, these customary methods are not satisfactory. In addition, since the afore-mentioned methods necessitate lar~e-scale facilities, they are not preferable from the economic viewpoi,nt~
In the accompanying drawings, Figure 1 shows the differ-' ' ' : ' ~ . . :
., 33~
ent changes in pH during the absorption of SO2 between two kindsof scrubbing solutions having different compositions;
Figure 2 shows the relation between the concentration ratio of S042 to S032 and the amount of gypsum separated out, and Figure 3 is a schematic outline illustratin~ a pxeferred embodiment of the present invention.
The inventors have found that under certain conditions, the alkali sulfate by-product may ~e double-decomposed with cal-cium carbonate to gypsum making it unnecessary to add a specialstep of removing alkali sulfate. Such conditions are that (1) alkali sul~osuccinate is used together with alkali sulfite as the SO2-absorbing agent, (2) the concentration of sulfit:e ion in the aqueous scrubbing solution ls controlled to be lower than 0.5 mol/kg and (3) the molar concentration ratio of sulfate ion to sulfite ion (SO4 /S032 ) is maintained at more than 3.
In the case of double decomposit1on of alkali hydrogen sulfite formed by the absorption of SO2 into an aqueous scrubbing solution of alkali sulfite with calcium carbonate, the concen-tration ratio of SO4 to SO3 in the aqueous scrubbing solution is required to be more than 3, preferably more than 4, in order to separate out gypsum in an equivalent amount to the amount of alkali sulfate formed in the system.
By contrast with this invention, in the case where only alkali sulfite is used as an SO2-absorbing agent, the concentra-tion of alkali sulfite is required to be 8 to 12~ by weight with .
, : .
, '. ': ' . : , .
33~
the concentration ratio of SO4 to SO3 more than 3, and accord-ingly, the total concentration of salts in the aqueolls solution becomes too large for salts to be deposited in the sys-tem, and in the case where an aqueous solut~on contains only alkali sulfo-succinate as an SO2~absorbing agent, the pH value of said aqueous solution drops rapidly when only a small amoun-t of SO2 is ab-sorbed.
~ ccordingly, in the case where only alkali sulfite is used as an absorbing agent with the ratio of sulfate to sulfite more than 3, the concentration of alkali sulfite must be less than 8% by weight, preferably less than 5~ by weight in the absorbing liquid. In such a case where the concentration of the absorbing agent is low, the amount of SO2 absorbable E?er unit amount of the scrubbing solution is small and it is necessary to provide a large amount of the scrubbing solution in order to raise the absorbing capacity. ~t is not preferable to use such a large amount of scrubbing solution.
In the method of the present invention, the concentration of sulfite ion in the scrubbing solution is controlled to less than 0.5 mol/kg and an alkali sulfosuccinate of a large solubil-ity in water is made co-present with the alkali sulfite. The alkali sulfosuccinate is equally ef~ective in absorbing SO2 and in forming aLkali hydrogen sulfite as alkali sulfite. The method of the present invention is advantageous in that by the co-presence of alkali sulfosuccinate with alkali sulfite, the possi-bility of salts separating out is removed and the concentration ratio of SO4 to SO3 can rlse above 3. Moreover, it becomes .: .
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, .
3~
possible to prevent the reduction of SO2-absorbing capacity of the scrubbing solution.
As a substance which may be co-present with alkali sul-fite in the aqueous scrubbing solution, alkali ac2tate, alkali propiona-te and others are sui-table candidates. However, it is inevitable that these alkali salts of organic acids to hydrolyze as a result of absorbing SO2, the organic acids so-formed being volatilized with the treated exhaust gas. Accordingly, it becomes necessary to wash th.e treated exnaust gas with water or an aqueous alkali solution to remove the ~olatilized organic acid, which renders the process more complicated.
Owiny to the molecular construction o~ sulfosuccinic acid, even after alkali sulfosuccinate is brought into contact with the exhaust gas containing SO2 and the aqueous scrubbing solution containing alkali sulfosuccinate absorbs the SO2, the free form of sulfosuccinic acid does not form in the scrubbing solution.
The sulfonic group of the acid remains always in ionic form (-SO3 M ) dissolved in the aqueous scrubbing solution. Accord-ingly, no free sulfosuccinic acid evaporates from the aqueous scrubbing solution when it is brought into contact with the ex-haust gas. This makes it unnecessary to install any additional step for the recovery of the free oryanic acid.
Accordiny to the present invention, it is possible to reduce the concentration of alkali sulfite in the scrubbing solution without reducing the SO2-absorbing capacity of the scrubbing solution, and the ratio o~ S042 to SO3 may he in-creased to more than 3 without making the total concentration of
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all salts large enough ~o cause them -to deposit. These possibil-ities are due to the co-presence of alkali sulfosuccinate with alkali sulfite in the scrubbing solution. Also in the case of of reaction of alkali sulfate with calcium carbonate, it is possible to obtain gypsum to the extent that it is not necessary to provide another means for removing the by-produced sulfate ions. In addition, although the rate of double decomposition by calcium carbonate is far slower than that by calcium hydroxide (Ca(OH)2), it is possible to obtain a practical and economical rate of double decomposition by lowering the p~i of the reaction solution. On an e~perimental scale, a reduc-tion of the pH by l accelerates the rate of decomposition by lO -times. According-ly, it is preferable to make the value of the pH of the reac-tion solution as low as possible- more preferably, to make the value of the p~ at the termination of the reaction to be lower than 6. Since, as mentioned above, alkali sulfosuccinate does not evaporate even at this value of pH, operating at such low : pH does not present a pro~lem.
Furthermore, the inventors have found also that although the ability of sodium sulfite (Na2S03) to absorb S02 is reduced very much in the lower range of pH of the scrubbing solution, the abiLity can be maintained sufficiently by addition of sulfo-succinate. FigO l shows these situations. In Fig. 1, :it is shown that in the absorbing liquid A in which the initial con-centration of (S03 ~ HS03 ) was 0.54 mol/kg, the pH shows a rapid reduction after absorbing 0.18 mol/kg of S02. However, it is also shown that in the absorbing liquid B in which the `' .
. . . :
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initial concentration of ~S03 r HS03 ) was 0.3? mol/kg and the remaining amount of 0.22 mol/kg was substituted by the equi-molar sulfosuccinate ion, the absorbing ability of the liquid s is maintained even after the absorption of more than 0.2 mol/-kg of S02 As mentioned above, it has been found by the inventorsthat the admixture of alkali sulfosuccinate into the scrubbing solution containing sodium sulfite gives a stabilized ability to absorb S02 to the liquid.
The scrubbing solution for S02 used in the present inven-tion is designed to contain 0.04 to 0.5 mol/kg of sulfite ion, 0.02 to 0.4 mol/kg of sulfosuccinate ion and 0.15 -to 1.4 mol/kg of sulfate ion with the ratio of S042 to S032 greater than 3.
The ratio of s~2 to S032 is determined adequately to be greater than 3 from the amount of alkali sulEate which is formed by oxidation in the scrubb~ng column. Since the amount of formation of alkali sulfate depends on the concentration of oxy~en in the exhaust gas to be treated, etc., the ratio of So~2 to S032 is decided at a value greater than 3, in order to separate out gypsum in the double decompos~tion in an amount cor-responding to the amount of formation of alkali sulf~te by oxi-dation in the scrubbing column. ~ig. 2 shows the relationship between the ratio of S042 to S032 and the ratio of CaS04 2H20 1/2 H20.
The invention will now be described and illustrated with , reference to the ~ollowing example, which is not to be construed ; as limiting upon the scope of the inven-tion.
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EXAMPI.E
An exhaust gas 1 from a heavy oil-burning boiler, con-taining 1,500 ppm of SO2 and 5% by volume of oxygen gas at a temperature of 150 C, was introduced into a scrubbing column 2 with a cross sectional area of 80 x 80 cm and a height of 5 m at a rate of 5,000 Nm3/hour. An aqueous scrubbing solution compris-cd an ac;ueous solution containing 0.218 mol/kg of ~odium sulfite, ~.2~0 .ol/k~ of sodium h~dro~en sulfite, 1.088 ~.ol/kg of soc.ium sulfate (calculated as anhydrous~ and 0.2586 mol/kg of sodium sulfosuccinate at a pH of 6.2. The aqueous scrubbing solution was brought into contact with the exhaust gas in the scrubbing column to absorb SO2 from the gas into the solution having the ratio of S042 to S032 at 5.0 and an absorption rate of 2,540 kg/hour.
The effluent 4 rom the bottom of the column 1 contained 0.075 mol/kg of Na2SO3, 0.45 moI~kg of NaHSO3, 1.106 mol/kg of Na2SO4 and 0.2586:mol/kg of sodium sulfosuccinate at a pH of 5.5.
A~part::of the effluent~was~aLrculated into the column 1 at a rate~o 7.5 m3/hour. During treatment of 5,000 Nm3jhour of the exhaus:t gas:,~about 44.6 mol/hour of Na2SO4 was formed in the oolumn 1.
The solution of 2,540 kg of the effluent 4 was introduced ;: ~ ;
into~à~ eactor 5~comprising three vessels connected to each ~ other and each~having a aapaci:ty of 1.1 m , and 352 mol/hour of ?;,'~ C ~ ~;6~was~admixed wlth the efluent in the reactor 5. The thus form~ed~cr~y-s~tals in the reactor:S were separ~ated by iltration ln~a~f:i~lter 7 and the~cryst~ls were washed with 47 kg~hour of ., , :
~ater, The fi}trate~of~a pH of 6.2 was returned to the aolumn 1.
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The cake 8 of the fll.tered and washed crystals was 93 kg/hour in weight (water con-tent of 50~) containing 35.3 kg/hour of CaS03.
1/2H20, 7.7 kg/hour of CaS04 2H20 and 3~4 kg/hour of CaC03.
As a result of the above-mentioned operation, it was found that the amount of sulfate ion in the scrubbing solution in circulation through the absorbing column 1 did not show any increase, and it was not necessary to prov.ide any special addi-tional step for removing the sulfate ion except the step for reacting the sulfate ion with CaC03.
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all salts large enough ~o cause them -to deposit. These possibil-ities are due to the co-presence of alkali sulfosuccinate with alkali sulfite in the scrubbing solution. Also in the case of of reaction of alkali sulfate with calcium carbonate, it is possible to obtain gypsum to the extent that it is not necessary to provide another means for removing the by-produced sulfate ions. In addition, although the rate of double decomposition by calcium carbonate is far slower than that by calcium hydroxide (Ca(OH)2), it is possible to obtain a practical and economical rate of double decomposition by lowering the p~i of the reaction solution. On an e~perimental scale, a reduc-tion of the pH by l accelerates the rate of decomposition by lO -times. According-ly, it is preferable to make the value of the pH of the reac-tion solution as low as possible- more preferably, to make the value of the p~ at the termination of the reaction to be lower than 6. Since, as mentioned above, alkali sulfosuccinate does not evaporate even at this value of pH, operating at such low : pH does not present a pro~lem.
Furthermore, the inventors have found also that although the ability of sodium sulfite (Na2S03) to absorb S02 is reduced very much in the lower range of pH of the scrubbing solution, the abiLity can be maintained sufficiently by addition of sulfo-succinate. FigO l shows these situations. In Fig. 1, :it is shown that in the absorbing liquid A in which the initial con-centration of (S03 ~ HS03 ) was 0.54 mol/kg, the pH shows a rapid reduction after absorbing 0.18 mol/kg of S02. However, it is also shown that in the absorbing liquid B in which the `' .
. . . :
, : ~' ' ` ; ' : , ' ;33~
initial concentration of ~S03 r HS03 ) was 0.3? mol/kg and the remaining amount of 0.22 mol/kg was substituted by the equi-molar sulfosuccinate ion, the absorbing ability of the liquid s is maintained even after the absorption of more than 0.2 mol/-kg of S02 As mentioned above, it has been found by the inventorsthat the admixture of alkali sulfosuccinate into the scrubbing solution containing sodium sulfite gives a stabilized ability to absorb S02 to the liquid.
The scrubbing solution for S02 used in the present inven-tion is designed to contain 0.04 to 0.5 mol/kg of sulfite ion, 0.02 to 0.4 mol/kg of sulfosuccinate ion and 0.15 -to 1.4 mol/kg of sulfate ion with the ratio of S042 to S032 greater than 3.
The ratio of s~2 to S032 is determined adequately to be greater than 3 from the amount of alkali sulEate which is formed by oxidation in the scrubb~ng column. Since the amount of formation of alkali sulfate depends on the concentration of oxy~en in the exhaust gas to be treated, etc., the ratio of So~2 to S032 is decided at a value greater than 3, in order to separate out gypsum in the double decompos~tion in an amount cor-responding to the amount of formation of alkali sulf~te by oxi-dation in the scrubbing column. ~ig. 2 shows the relationship between the ratio of S042 to S032 and the ratio of CaS04 2H20 1/2 H20.
The invention will now be described and illustrated with , reference to the ~ollowing example, which is not to be construed ; as limiting upon the scope of the inven-tion.
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; ~ - 7 -`
~, ` :
EXAMPI.E
An exhaust gas 1 from a heavy oil-burning boiler, con-taining 1,500 ppm of SO2 and 5% by volume of oxygen gas at a temperature of 150 C, was introduced into a scrubbing column 2 with a cross sectional area of 80 x 80 cm and a height of 5 m at a rate of 5,000 Nm3/hour. An aqueous scrubbing solution compris-cd an ac;ueous solution containing 0.218 mol/kg of ~odium sulfite, ~.2~0 .ol/k~ of sodium h~dro~en sulfite, 1.088 ~.ol/kg of soc.ium sulfate (calculated as anhydrous~ and 0.2586 mol/kg of sodium sulfosuccinate at a pH of 6.2. The aqueous scrubbing solution was brought into contact with the exhaust gas in the scrubbing column to absorb SO2 from the gas into the solution having the ratio of S042 to S032 at 5.0 and an absorption rate of 2,540 kg/hour.
The effluent 4 rom the bottom of the column 1 contained 0.075 mol/kg of Na2SO3, 0.45 moI~kg of NaHSO3, 1.106 mol/kg of Na2SO4 and 0.2586:mol/kg of sodium sulfosuccinate at a pH of 5.5.
A~part::of the effluent~was~aLrculated into the column 1 at a rate~o 7.5 m3/hour. During treatment of 5,000 Nm3jhour of the exhaus:t gas:,~about 44.6 mol/hour of Na2SO4 was formed in the oolumn 1.
The solution of 2,540 kg of the effluent 4 was introduced ;: ~ ;
into~à~ eactor 5~comprising three vessels connected to each ~ other and each~having a aapaci:ty of 1.1 m , and 352 mol/hour of ?;,'~ C ~ ~;6~was~admixed wlth the efluent in the reactor 5. The thus form~ed~cr~y-s~tals in the reactor:S were separ~ated by iltration ln~a~f:i~lter 7 and the~cryst~ls were washed with 47 kg~hour of ., , :
~ater, The fi}trate~of~a pH of 6.2 was returned to the aolumn 1.
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. : . .. . . ~
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The cake 8 of the fll.tered and washed crystals was 93 kg/hour in weight (water con-tent of 50~) containing 35.3 kg/hour of CaS03.
1/2H20, 7.7 kg/hour of CaS04 2H20 and 3~4 kg/hour of CaC03.
As a result of the above-mentioned operation, it was found that the amount of sulfate ion in the scrubbing solution in circulation through the absorbing column 1 did not show any increase, and it was not necessary to prov.ide any special addi-tional step for removing the sulfate ion except the step for reacting the sulfate ion with CaC03.
:~ _ 9 _ : .
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of removing sulfur dioxide from an exhaust gas containing the same comprising the steps of:
(a) bringing said exhaust gas into contact with an aqueous scrubbing solution containing 0.04 to 0.5 mol/kg of alkali sulfite, 0.15 to 1.4 mol/kg of alkali sulfate, and 0.02 to 0.4 mol/kg of alkali sulfosuccinate to absorb said sulfur dioxide in the forms of alkali sulfite, alkali hydrogen sulfite and alkali sulfate;
(b) converting said alkali sulfite, alkali hydrogen sulfite and alkali sulfate contained in at least a portion of said aqueous scrubbing solution which was used in step (a) with calcium carbonate, respectively to calcium sulfite, calcium hydrogen sulfite and calcium sulfate while maintaining the molar concentration ratio of sulfate ion to sulfite ion of said aqeous scrubbing solution at a value of more than 3;
(c) separating by filtration said calcium sulfite and calcium sulfate from the treated aqueous solution in step (b);
and (d) recycling the filtrate obtained in step (c) for use as the scrubbing solution in step (a).
(a) bringing said exhaust gas into contact with an aqueous scrubbing solution containing 0.04 to 0.5 mol/kg of alkali sulfite, 0.15 to 1.4 mol/kg of alkali sulfate, and 0.02 to 0.4 mol/kg of alkali sulfosuccinate to absorb said sulfur dioxide in the forms of alkali sulfite, alkali hydrogen sulfite and alkali sulfate;
(b) converting said alkali sulfite, alkali hydrogen sulfite and alkali sulfate contained in at least a portion of said aqueous scrubbing solution which was used in step (a) with calcium carbonate, respectively to calcium sulfite, calcium hydrogen sulfite and calcium sulfate while maintaining the molar concentration ratio of sulfate ion to sulfite ion of said aqeous scrubbing solution at a value of more than 3;
(c) separating by filtration said calcium sulfite and calcium sulfate from the treated aqueous solution in step (b);
and (d) recycling the filtrate obtained in step (c) for use as the scrubbing solution in step (a).
2. The method according to Claim 1, wherein said alkali sulfite is a member selected from the group consisting of sodium sulfite, ammonium sulfite and a mixture thereof.
3. The method according to Claim 1, wherein said alkali sulfosuccinate is a member selected from the group consisting of sodium sulfosuccinate, ammonium sulfosuccinate and a mixture thereof.
4. The method according to Claim 1 or 3, wherein said alkali sulfosuccinate is sodium sulfosuccinate.
5. The method according to Claim 1, wherein the molar concentration ratio of sulfate ion to sulfite ion in said aqueous scrubbing solution is maintained at a value of more than 4.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP53136532A JPS5853565B2 (en) | 1978-11-06 | 1978-11-06 | Desulfurization method |
| JP136532/78 | 1978-11-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1148331A true CA1148331A (en) | 1983-06-21 |
Family
ID=15177380
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000338335A Expired CA1148331A (en) | 1978-11-06 | 1979-10-24 | Method of removing sulfur dioxide |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS5853565B2 (en) |
| CA (1) | CA1148331A (en) |
| DE (1) | DE2943152C2 (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS51151697A (en) * | 1975-06-23 | 1976-12-27 | Kureha Chem Ind Co Ltd | Method for removal of sulfur dioxide in exhaust gas |
| JPS5825492B2 (en) * | 1975-08-05 | 1983-05-27 | 呉羽化学工業株式会社 | Iousankabutsunojiyokiyohouhou |
-
1978
- 1978-11-06 JP JP53136532A patent/JPS5853565B2/en not_active Expired
-
1979
- 1979-10-24 CA CA000338335A patent/CA1148331A/en not_active Expired
- 1979-10-25 DE DE19792943152 patent/DE2943152C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2943152C2 (en) | 1984-09-06 |
| JPS5561923A (en) | 1980-05-10 |
| JPS5853565B2 (en) | 1983-11-30 |
| DE2943152A1 (en) | 1980-05-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |